Field of the Invention
[0001] The present invention relates to a method and system for locating user equipment
within a communications network.
Background of the Invention
[0002] A cellular telecommunications system is a communication system that is based on use
of radio access entities and/or wireless service areas. The access entities operate
over respective coverage areas that are typically referred to as cells. Examples of
cellular telecommunications systems include standards such as the GSM (Global System
for Mobile communications) or various GSM based systems (such as GPRS: General Packet
Radio Service), AMPS (American Mobile Phone System), DAMPS (Digital AMPS), WCDMA (Wideband
Code Division Multiple Access), TDMA/CDMA (Time Division Multiple Access / Code Division
Multiple Access) in UMTS (Universal Mobile Telecommunications System), CDMA 2000,
i-Phone and so on.
[0003] In a cellular system, a base transceiver station (BTS) provides a wireless communication
facility that serves mobile stations (MS) or similar wireless user equipment (UE)
via an air or radio interface within the coverage area of the cell. As the approximate
size and the shape of the cell is known, it is possible to associate the cell to a
geographical area. Each of the cells can be controlled by an appropriate controller
apparatus.
[0004] Elements of the cellular network can be employed for provision of location information
concerning a mobile station and the user thereof. More particularly, the cells or
similar geographically limited service areas facilitate the cellular telecommunications
system to produce at least a rough location information estimate concerning the current
geographical location of a mobile station, as the cellular telecommunications system
is aware of the cell with which a mobile station currently associates. Therefore it
is possible to conclude from the location of the cell the geographical area in which
the mobile station is likely to be at a given moment. This information is available
also when the mobile station is located within the coverage area of a visited or "foreign"
network. The visited network may be capable of transmitting location information of
the mobile station back to the home network, e.g. to support location services or
for the purposes of call routing and charging.
[0005] A location service feature may be provided by a separate network element such as
a location server which receives location information from at least one of the controllers
of the system. If no further computations and/or approximations are made, this would
give the location to an accuracy of one cell, i.e. it would indicate that the mobile
station is (or at least was) within the coverage area of a certain cell.
[0006] However, the accuracy of the location determination may be improved by utilising
results of measurements which define the travel time (or travel time differences)
of the radio signal sent by a mobile station to the base station. More accurate location
information may be obtained through e.g. by calculating the geographical location
from range or range difference (RD) measurements. All methods that use range difference
(RD) measurements may also be called TDOA (time difference of arrival) methods (mathematically
RD = c * TDOA, wherein c is the signal propagation speed). Observed time difference
(OTD), E-OTD (Enhanced OTD) and TOA (time of arrival) are mentioned herein as examples
of technologies that are based on the RD measurements.
[0007] The difference between the TOA (time of arrival) and the E-OTD is in that in the
TOA the mobile station sends the signal and network makes the measurements, whereas
in the E-OTD the network sends the signals and the mobile station measures them. The
mobile stations are provided with appropriate equipment and software to provide information
on which the positioning of the mobile station can be based on. The mobile station
may communicate the information via the base station to an appropriate network element
that may use the information in a predefined manner.
[0008] It is also possible to form RD measurements based on other sources, e.g. from GPS
(Global Positioning System) pseudo-range measurements.
[0009] Therefore it is evident that there exist a variety of techniques for determining
the position of the mobile station with a cell. In many of these systems, for example
TDOA, the position measurement signals are received by LMUs (Location Measuring Units)
from the MS and then sent to a SMLC (Serving Mobile Location Centre) that calculates
the location of the MS.
[0010] Accurate positioning information is particularly required for emergency services,
so that an emergency service provider is able to determine an accurate estimate of
the current location of a MS.
[0011] The United States Federal Communication Commission (FCC) has mandated that wireless
service providers have to implement location technologies that can locate wireless
phone users who are calling to emergency numbers. In particular, the FCC's Third Report
and Order (FCC 99-245) specifies the following standards for Phase II location accuracy
and reliability:
- For network based solutions:- 100 meters for 67% of calls, and 300 meters for 95%
of calls;
- For handset based solutions:- 50 meters for 67% of calls, and 150 meters for 95% of
calls.
[0012] The ANSI (American National Standards Institute) specification TIA/EIA/J-STD-036-A
having the title "Enhanced Wireless 9-1-1 Phase 2" defines for ANSI 41 and GSM systems
how initial and updated location information is determined and routed to a PSAP (Public
Safety Answering Point) during an emergency call. However, this routing is based on
cell level location information, wherein a MSC (Mobile Switching Centre) routes all
emergency calls from certain cells to a particular PSAP.
[0013] However, this solution is not optimised in situations in which there are two or more
PSAP service areas that over lap with the coverage of a single cell, and the problem
becomes even more acute when the cell's are setup to have large coverage areas.
[0014] The present invention is related to allowing emergency calls to be routed based on
geographical position within a cell.
[0015] Therefore there is a need for an improved manner of routing emergency calls based
on the geographical location.
Summary of the Invention
[0016] It is an aim of embodiments of the present invention to address one or more of these
problems using existing functionality.
[0017] According to one aspect there is provided a method for establishing an emergency
call between a user equipment within a radio coverage area and one of at least two
points able to answer the call, the method comprising: receiving said emergency call
request; determining a first estimate of the position of said user equipment within
said coverage area; interrupting said call establishment by triggering a control point;
and using the control point to select, based on said first position estimate, which
one of said at least two answering points the call is established with.
[0018] Preferably said at least one answering point has been selected, said switching centre
resumes said call establishment and a second more accurate position estimate is determined
and sent to said selected answering point.
[0019] Preferably non-call associated signalling is used wherein messages used to select
the at least one of the two answering points during call establishment are separate
from the messages used for the established call itself.
[0020] Preferably said selecting is done using the control point for translates the first
position estimate which is a geographical position into a routing number of the selected
answering point.
[0021] Preferably the first position estimate is determined by using an identifier of said
radio coverage area and timing advance information.
[0022] According to a second aspect of the invention there is provided a communications
system for establishing an emergency call between a user equipment and an emergency
call processing centre, the system being configured to establish the call according
to a method as set out above.
[0023] According to a third aspect of the invention there is provided a communications network
for establishing an emergency call between a user equipment within a radio coverage
area and one of at least two points able to answer the call, the network comprising:
a base controller for controlling a base transceiver that provides said radio coverage
area; a switching centre for receiving said emergency call request; a location centre
for determining a first estimate of the position of said user equipment within said
coverage area; and a control point for selecting which of said at least two answering
points the call is established with based on said first position estimate and wherein
the control point is triggered by interrupting said call establishment.
[0024] Preferably when said at least one answering point has been selected, said switching
centre resumes said call establishment and a second more accurate position estimate
is determined and sent to said selected answering point.
[0025] Preferably the switching centre comprises means for identifying events during the
call establishment.
[0026] Preferably said identifying means is arranged to identify the event when the first
estimated position has been determined, and when said event is identified said call
establishment is interrupted and said control point is triggered.
[0027] Preferably the at least two answering points are emergency call processing centres.
[0028] Preferably the control point is a GSM service control point.
[0029] Preferably the network further comprising a gateway location centre for providing
an interface between said network and said at least two answering points.
[0030] Preferably the control point comprises a coordinate routing database for mapping
a geographical position of said first position estimate to said selected answering
point.
[0031] Preferably the location centre is located within said base controller. Alternatively,
the location centre may be located separate from said base controller.
Brief Description of Drawings
[0032] For a better understanding of the present invention and to show how the same may
be carried into effect, reference will now be made by way of example to the accompanying
drawings in which:
Figure 1 shows the generic LCS logical architecture;
Figure 2 shows the system level of the LCS arrangement for GSM and UMTS radio access
networks;
Figure 3 shows a network reference model for supporting emergency services;
Figure 4 shows overlapping PSAP regions and radio cell coverage according to an embodiment
of the present invention;
Figure 5 shows a flow-chart of a known NCAS method of using the initial position for
routing and processing the call;
Figure 6 shows a flow chart of an alternative embodiment of the present invention;
and
Figure 7 shows a flow chart describing in more detail some of the steps of Figure
6.
Description of Preferred Embodiments of the Invention
[0033] Figure 1 shows the generic LCS (Location Services) logical architecture as specified
in the 3GPP TS 03.71 Release 99 specification for the Functional Descriptions of Location
Services.
[0034] An MS 2 is shown connected to a BTS 4 having a particular cell coverage dependant
on the transmission power of the BTS 4. The BTS 4 can have the LMU functionality in
the BTS itself or separate. The BTS 4 is connected to a BSC 6 (Base Station Controller),
which typically controls a plurality of BTSs each having their own cell coverage.
The BSC 6 can be connected to an SMLC 16 (Serving Mobile Location Centre) or to an
MSC 8. The MSC 8 typically controls a plurality of BSCs and has a VLR (Visitor Location
Register), which maintains a database of the details of the MS when entering into
a visited network.
[0035] The SMLC resides either at the core network level or the radio level and has the
functionality for receiving locations measurement signals from the MS 2, and the SMLC
is able to compute the final geographical location estimate and the accuracy of the
MS 2 within a particular cell. The SMLC 16 may be a standalone unit and connected
to the BSC 6 in a BSS (Base Station Subsystem) based SMLC, or to the MSC 8 in a NSS
(Network Service Subsystem) based SMLC. Alternatively, the SMLC may be part of another
network entity, e.g. the BSC.
The MSC 8 is also connected to a GMLC 10. Using information that it stores or has
access to the GMLC authenticates the LCS client 18 that is requesting the position
of a subscriber of the system. The GMLC 10 can identify the subscriber by an identifier
that specifies the subscriber or the hardware he is using to access the system (e.g.
MSISDN or IMSI codes). Using such an identifier it can query the HLR 14 (Home Location
Register) to determine in which MSCs (or equivalent's) coverage area the subscriber
is located. Such a query will yield the address of the MSC or the address of an equivalent
device such as an SGSN. The HLR is aware of the current (for instance) MSC and VLR
from previous location update procedures. When a location request is received by the
MSC the MSC will check for any subscriber-specific LCS privacy restrictions that might
be in place, and if the request is not barred by such restrictions it proceeds with
the positioning request towards the radio network or SMLC.
[0036] The GMLC 10 can also be connected to a gsm(SCF) 12 (GSM Service Control Function)
block, which will be described in more detail later.
[0037] In any event, it should be appreciated that the functionality shown in Figure 1 is
moveable, so that although the external client is responsible for initiating the position
location request, according to a preferred embodiment of the present application,
the functionality of the external client 18 can be thought of as moving into the MSC
8. Therefore, the MSC initiates the location request.
[0038] The MSC 8 sends the location request to the relevant BSC 6. In a preferred embodiment,
the functionality of the SMLC 16 resides with the BSC, and therefore the geographical
position of MS 2 can be computed within the radio network using any of the known positioning
methods, for example TDOA. Once the geographical location has been calculated it is
return via the MSC 8 to the GLMC 10.
[0039] Figure 2 shows a system level of the LCS arrangement for GSM and UMTS radio access
networks as specified in the 3GPP TS 23.271 Release 4 specification for the UMTS (Universal
Mobile Telecommunications system) Functional Descriptions of Location Services. This
diagram shows that the standard has evolved to take into account 3G (Third Generation)
UMTS networks, which communicate over a UTRAN 22 (UMTS Radio Access Network) with
the core network, as well as reinforcing the fact that legacy 2G (second Generation)
GSM networks communicate over the GERAN (GSM/EDGE Radio Access Network). Therefore,
depending on the radio network, the functionality of the SMLC as referred to in relation
to Figure 1 can reside in either the GERAN 20 or the UTRAN 22. Most of the core functionality
is the same, wherein the same reference numerals refer to the same functionality as
described in figure 1, for example, the GMLC 10, the external LCS client 18, the gsmSCF,
etc.
[0040] In an embodiment of the present invention, the service which is requesting the positioning
information is an emergency service. Figure 3 shows an example of a network reference
model for supporting emergency services as specified in the TIA/EIA/J-STD-036-A document.
The BSS (Base Station subsystem) 30 should be understood to refer to the radio network
comprising the BSCs 6 and BTSs 4. The MS can be connected to a visited PLMN network
controlled by a visited MSC 8, which in turn is connected to a GMLC 10 and through
an emergency services network 32 to a PSAP point 28.
[0041] The emergency services network 32 comprises an ESNE 24 (Emergency Service Network
Entity) and an ESME 26 (Emergency Service Message Entity). At this point, it will
be useful to understand the difference between CAS (Call Associated Signalling) and
NCAS (Non-Call Associated signalling), which are both techniques for passing location
information between the wireless network and the PSAP. In CAS signalling, information
is passed within the same messages used to setup and control an emergency call, whereas
for NCAS signalling the messages containing location information are passed separate
from the call itself.
[0042] Broadly speaking, the ESME routes and processes the out-of band messages relating
to emergency calls and for NCAS this can be thought of as dealing with the messages
containing the location information, whereas the ESNE routes and processes the voice
band portion of the call and for NCAS can be thought of as dealing with the call itself.
[0043] The location information can be used for two purposes. Firstly to route the call
to the appropriate PSAP and secondly used by the operator of the emergency service
to locate the caller geographically and dispatch the relevant emergency services.
For example, the position information typically contains a given latitude and longitude,
which can be translated using a database into the nearest known street address or
used to plot the position of the MS on a map with other information like building
names, business names, landmarks, etc.
[0044] The Base Station Subsystem (BSS) 30 receives the emergency call from the MS and notifies
the VMSC 8. To achieve this, the MS first establishes a radio interface connection
with the BSC. Then the MS sends a connection management service request to the BSC,
which forwards that to the MSC. At this point an A-interface connection is created
between the BSC and the MSC. After that the MS sends a call setup request to the MSC,
which is relayed transparently through the BSC. The BSS is also involved in the handling
of certain positioning procedures. As a generic handling procedure, the BSS is equipped
to collect/determine timing advance (TA) information for communications between the
MS and it and neighbouring cells, together with receive signal strength levels for
such communications. The BSS may determine the location of the MS based on this location.
Alternatively, the BSS may transmit TA information for it and neighbour cells, or
just for its cell to another entity that can then determine the location. For example,
the TA information could be sent to the SMLC to assist in obtaining a position estimate.
Specific BSS functionality in positioning procedures is specified in 3GPP TS 03.71
or 3GPP TS 43.059.
[0045] The CI (Cell Identifier) method is able to identify the coordinates of the radio
coverage area cell of the serving BTS, and that the coverage area of the cell is divided
into sectors so that this method can identify which sector of the cell the MS is located.
[0046] The CI + TA (Timing Advance) method is slightly more accurate in that the location
of the MS within the cell can be even more accurately estimated using TA signals sent
between the MS and the BTS, in which the network is able to estimate the distance
between the MS from the BTS by calculating the time it takes for signals transmitted
from the MS to arrive at the BTS and/or vice versa.
[0047] Other methods for example, include the CI+TA+Rx (Receiver) positioning method where,
in addition to having the cell/sector identifier (and the coordinates of the cell)
and the timing advance information, a received signal level is used to locate the
MS. That is, the MS also monitors the power of the signals received from neighbouring
BTSs (i.e. each providing their own cell coverage). It follows that the geographical
position can be more accurately determined using a line of sight principle so that
the MS will be closest to the neighbouring BTS whose signals, received by the MS,
are the strongest.
[0048] The GMLC 10 also handles requests for the MS from the ESME such as the updated (current)
or last known position. The GMLC stores the initial position estimate to support NCAS
signalling.
[0049] Figure 4 shows an example of PSAP coverage having difference ESZs (Emergency Service
Zones). Two BTS elements 4 and 4' are indicated, each having their own radio cell
coverage 40 and 40' respectively. Also, two arcs 26 and 28 represent the coverage
zone of a first PSAP 42 and a second PSAP 44 respectively
[0050] It must be noted that Figure 4 is a conceptual diagram and the arcs shown by the
lines 36 and 38 representing the emergency zones are not radio coverage areas. Instead
these arcs 36, 38 represent different geographical areas, each of which is covered
by particular PSAP. That is, arc 36 is the geographical border of the ESZ controlled
by PSAP1 42 and arc 38 is the geographical border of the ESZ controlled by PSAP2 44.
However, if the radio cell coverage crosses geographical borders defined for each
PSAP, then more than one PSAP covers a particular cell.
[0051] An embodiment of the present invention optimises the routing of the emergency services
call to the relevant PSAP. To do this, it is necessary to obtain a more accurate position
estimation of the MS 2 within the cell 40'. If an estimate of the position of the
MS 2 within the cell is provided, then it is possible to determine that PSAP 2 is
where the call should be routed to since this lies within ESZ2.
[0052] The TIA/EIA/J-STD-036-A standard is concerned with determining an "initial position"
estimate of the MS and using this information for both processing the call and routing
it to a PSAP based on this initial position. At present this only applies to the CAS
method in GSM. An example of a flow chart showing the process for an NCAS case is
shown in Figure 5.
[0053] The messages referred to with the numerals (a) through (I) refer to the different
messages and will now be described. At step (a) the MS invokes an emergency services
call. This triggers determination of the initial position of the MS by the sending
of a Perform Location message to the SMLC in step (c). At step (b) the "Call Setup"
message extends the call to the ESNE for processing the call by the emergency service.
At step (c) a "perform location [QoS]" message is sent from the MSC to the SMLC, requesting
the computation of the initial position within a particular accuracy range given by
the QoS (Quality of Supply) requirement. If the SMLC resides in the BSS then the MSC
would send this message to the BSC, which would send it further to the SMLC. At step
(d) messages for specific positioning methods in the radio network are exchanged,
for example TDOA, after which time the initial position is estimated and returned
by the SMLC to the MSC at step (e). At step (f) the initial position is sent from
the MSC to the GMLC and acknowledged at step (g). At step (h), the ESME requests the
initial position of the MS stored in the GLMC and this is supplied to the ESME at
step (i). At step j, the emergency call is released, which frees up a significant
amount of dynamic information that is typically setup for each emergency call. This
frees the valuable resources of the emergency services network associated with a particular
PSAP to deal with other calls. At steps (k) and (I) any information relating to the
call including the initial position is released from the storage of the GMLC.
[0054] One disadvantage of this method is that the call must be extended to the ESNE before
the geographical location is known to any better accuracy than the simply which cell
the MS is in. If initial position were to be used for routing purposes then the Call
Setup message (step (b)) should be delayed until the MSC had got a response to the
positioning request (step (e)). The positioning methods used in determining an initial
position need to be very accurate in order to satisfy the strict FCC requirements.
However, another requirement is that the emergency call should be routed to the relevant
PSAP as soon as possible.
[0055] Therefore, an embodiment of the present invention makes a distinction between a position
estimate made for routing purposes, which will be referred to herein as the "interim
position", and the more accurate "initial position" used to indicate the location
of the MS for the FCC requirements. The interim position is still a far more accurate
estimate of the position of the MS as compared to the cell-level positioning methods
of the prior art, but is slightly less accurate than the initial position. The benefit
achieved by using a slightly less accurate positioning method in estimating the interim
position is that the relevant PSAP can be selected more quickly, which optimises the
system as a whole particularly when there is more than one PSAP covering a cell. The
interim position can be determined by a method not requiring time consuming measurement
procedures. An example of a method to be used for determining the interim position
is CI + TA (Cell Identity with Timing Advance).
[0056] An embodiment of the present invention is shown in Figure 6. In this embodiment,
the interim position as a geographical location is determined (step b) before the
initial position as a geographical location is determined (step g). Figure 7 is a
flow chart illustrating a generic procedure to determine location estimate as a geographical
location, being it either interim or initial position of the caller.
[0057] If the emergency call should be routed based on geographical position, then the interim
position of the calling mobile station is determined. The required accuracy for the
interim position represents the accuracy that is sufficient for call routing to the
relevant PSAP. That is, the interim location is a more accurate position estimate
of the MS as compared to the less accurate method of using the base station's location
of the serving cell. This procedure is now described in more detail Figure 7.
[0058] Figure 7 shows that at step (a) the MSC sends a request to determine the MS's geographical
location to the BSC in GSM or RNC (Radio Network controller) in UMTS. The request
includes the requested QoS for positioning, i.e. the accuracy expected by the MSC.
The request may also carry other information such as the Location Services client
type (e.g. emergency services client type). In GSM this message is the "BSSMAP Perform
Location Request" as described in the 3GPP TS 08.08/48.008 standard. In UMTS the corresponding
message is "RANAP Location Reporting Control" as described in 3GPP TS 25.413.
[0059] At step (b) the BSC (or RNC) forwards the request to the SMLC, which is responsible
for actually calculating the interim position. As described before, in GSM the SMLC
functional entity may be part of the BSC, or a standalone network element. In the
latter case the messages used are "BSSMAP-LE Perform Location Requests" as described
in 3GPP TS 09.31/49.031. In 3GPP releases 98 and 99 the SMLC may be located in the
core network (or network sub-system, NSS), in which case the MSC sends location requests
using the BSSMAP-LE protocol (3GPP TS 09.31/49.031) directly to the SMLC. However,
in 3GPP Rel-4 and later releases the SMLC always resides in the radio network, BSS
or GERAN.
[0060] In UMTS, the SMLC functional entity is part of the RNC in 3GPP Rel-4, thus this message
is within the RNC's internal communication. From 3GPP Rel-5 onwards the SMLC may also
be a standalone element within the UTRAN.
[0061] At step (c) the messages for individual positioning methods are transferred, if the
used method requires some information or measurement results from the MS or the radio
network controller. For GSM system these are described in 3GPP TS 03.71 (3GPP R98
and R99) or 3GPP TS 43.059 (3GPP Rel-4 and later). For UMTS system these are described
in 3GPP TS 25.305. It should be noted that after receiving the location request the
SMLC may already have information necessary for determining position, e.g. current
cell identity and timing advance, without any further message exchange required with
other entities.
[0062] At step (d) the SMLC returns the location estimate to the BSC (or RNC).
[0063] In GSM if the SMLC is a standalone network element, the message is a "BSSMAP-LE Perform
Location Response". In 3GPP releases 98 and 99 if the SMLC is located in the core
network the SMLC sends this location response message directly to the MSC.
[0064] In UMTS the SMLC functional entity is part of the RNC, thus this message is communicated
internally within the RNC.
[0065] At step (e) the BSC (or RNC) returns the interim position estimate to the MSC. In
GSM this message is a "BSSMAP Perform Location Response". In UMTS the corresponding
message is a "RANAP Location Report".
[0066] In an alternative embodiment of the present application the SMLC is used to determine
an "interim position" before the "initial position" is determined. The interim position
is determined using a shortened and less accurate procedure than is used for determining
the initial position.
[0067] The gsmSCF represents functionality which is able to perform control algorithms if
a certain event in the BCSM (Basic Call State Model) is triggered. In particular,
the MSC is imbued with SSF (Service Switching Function) functionality for communicating
with the gsmSCF. The SSF and gsmSCF are well known functional entities defined in
the CAMEL (Customized Applications for Mobile Network Enhanced Logic) standards.
[0068] This embodiment comprises the following steps (a) to (o) as described in figure 6.
- (a). The MS invokes an emergency services call.
- (b). If the emergency call should be routed based on geographical position, then the
MSC initiates determination of interim position using signal flow presented in figure
7. The requested QoS is the accuracy requirement for the interim location that is
used for routing the emergency call. In order to fulfil time constraints for determining
interim position the SMLC may use for example CI + TA positioning method or similar.
- (c). According to an embodiment of the present invention, if the emergency call should
be routed based on geographical position, then the MSC contains SSF (Service Switching
Functionality) which contains DP's (Detection Points) identifying various events of
the call processing within the MSC. In particular, when the interim position has been
determined the detection point "Collected_Info", which is described in 3GPP TS 23.078,
is triggered. When the detection point is triggered, the MSC sends a CAP (CAMEL Application
Part) message to the gsmSCF indicating that the interim position has been estimated
and what that estimate is. In particular, the "CAP Initial DP message" comprises for
example, Called Party Number, Calling Party Number, IMSI (International Mobile Subscriber
Identity), Geographical Information and Location Number.
[0069] Therefore, the Geographical Information will contain the interim position received
by the MSC at step (b). The gsmSCF may assign a new routing number based on the Geographical
Information.
(d). The gsmSCF may establish a monitoring relationship by arming one or more detection
points. This may be needed in order to receive notification at release of the emergency
call. Thus, the gsmSCF 12 can request that when certain events are encountered during
call processing of the SSF in the MSC 8, that these events are notified to the gsmSCF.
For example, the "CAP Request Report BCSM event" can arm a detection point in the
BCSM (Basic Call State Model) of the SSF in MSC 8 to notify the gsmSCF when the call
is released (see step q below). In this way, when notification of emergence call release
is received, valuable resources of the SCP (e.g. a unique ESRK value reserved for
the call) can be freed.
(e). The gsmSCF requests the MSC to continue call processing with modified information.
That is, the geographical position containing the interim position can be translated
from a latitude/longitude co-ordinate to a new destination address, to determine which
PSAP to route the emergency call to. In one embodiment of the present invention, the
translation can be performed by a CRDB (Coordinate Routing Database). In this way
the gsmSCF can supply a new routing destination for the call, wherein the "CAP Connect"
message can identify the relevant PSAP with new destination routing address, which
is for example an ESRK (Emergency Services Routing Key) allocated to particular the
emergency call as shown, or alternatively ESRD (Emergency Services Routing Digits)
that identifies also identifies a base station, cell site or sector.
(f). The MSC extends the call to the ESNE associated with the PSAP identified by the
interim position of the MS. The call setup should include at a minimum either a callback
number (dialable or non-dialable) plus the ESRD or ESRK.
(g). The MSC sends a request to perform initial location determination using a requested
QoS2. QoS2 is in line with the FCC regulations and therefore is more accurate than QoS1. The requested QoS2 is the accuracy requirement for the initial position that is reported to the GMLC
to determine more accurately the position of the MS. Messages for initial positioning
methods are transferred as for the known methods as described in 3GPP TS 43.059, for
example E-OTD. Therefore the initial position method of steps proceeds as before (see
Figure 7).
[0070] It should be noted however, that at point (m), a call release event of the BCSM in
the SSF/MSC is encountered, which was armed earlier at step (d). Therefore, the gsmSCF
is informed that the call is released and the gsmSCF 12 is then able to free up resources
related to the emergency call.
[0071] The embodiments of the present invention firstly determine the interim position at
emergency call setup and then interrupt call establishment at the MSC by sending the
interim position to an SCP (Service Control Point), which is the more generic term
for the gsmSCF 12 functionality. The SCP then determines the routing address of the
relevant PSAP based on the interim position. The SCP supplies the routing address
to MSC, which routes the call to the PSAP. Finally, the initial position which satisfies
the FCC requirements is determined as before and sent via the GMLC to the PSAP so
that a more accurate location of the caller may be dispatched by the emergency services
network.
[0072] Therefore, the gsmSCF is used to control the routing of the emergency call to the
relevant PSAP based on an interim position estimate. The gsmSCF allows the described
embodiments to decouple the routing of the call from the GMLC and therefore the GMLC
does not need to be re-designed.
[0073] It needs to be appreciated that the described embodiments are particularly useful
in that they have minimal impact on existing network entities. The described embodiments
use standardised interfaces and routing is based on an interim position performed
using the control functionality afforded by the gsmSCF, which is an existing entity
in 3GPP network architecture. That is, the CAMEL framework provides a standardised
interface and protocol for establish control relationships between the MSC/SSF and
the gsmSCF.
[0074] It should be appreciated that the visited network is able to perform call routing
for at least the circuit-switched domain of GSM and UMTS. Even if the subscriber has
some CAMEL services, it is preferred that triggering for emergency calls is based
on information about the currently visited network of the subscriber. This may call
for a modification of the CAMEL specification. Such information about the currently
visited network could be, for example, an indication that in the visited network the
emergency call should be routed based on interim position. Thus, routing of an emergency
can be done by the visited network even if the CAMEL SCP is used to control the routing.
[0075] It should also be appreciated that the present invention is primarily intended for
use in GSM or WCDMA techniques, but is not necessarily limited to these networks.
According to some, but not necessarily all, embodiments of the invention there is
provided a method for establishing an emergency call between a user equipment within
a radio coverage area and one of at least two points able to answer the call, the
method comprising: receiving said emergency call request; determining a first estimate
of the position of said user equipment within said coverage area; interrupting said
call establishment by triggering a control point; and using the control point to select,
based on said first position estimate, which one of said at least two answering points
the call is established with.
when said at least one answering point has been selected, said switching centre may
resume said call establishment and a second more accurate position estimate may be
determined and sent to said selected answering point.
[0076] Non-call associated signaling may be used and messages used to select the at least
one of the two answering points during call establishment may be separate from the
messages used for the established call itself.
[0077] The selecting may be done using the control point for translating the first position
estimate which may be a geographical position into a routing number of the selected
answering point.
[0078] The first position estimate may be determined by using an identifier of said radio
coverage area and timing advance information.
[0079] According to some, but not necessarily all, embodiments of the invention there is
provided a communications system for establishing an emergency call between a user
equipment and an emergency call processing centre, the system being configured to
establish the call according to the method as described in any of the preceding paragraphs.
[0080] According to some, but not necessarily all, embodiments of the invention there is
provided a communications network for establishing an emergency call between a user
equipment within a radio coverage area and one of at least two points able to answer
the call, the network comprising: a base controller for controlling a base transceiver
that provides said radio coverage area; a switching centre for receiving said emergency
call request; a location centre for determining a first estimate of the position of
said user equipment within said coverage area; and a control point for selecting which
of said at least two answering points the call is established with based on said first
position estimate and wherein the control point is triggered by interrupting said
call establishment.
[0081] When said at least one answering point has been selected, said switching centre may
resume said call establishment and a second more accurate position estimate may be
determined and sent to said selected answering point.
[0082] The switching centre may comprise means for identifying events during the call establishment.
[0083] The identifying means may be arranged to identify the event when the first estimated
position has been determined, and when said event is identified said call establishment
may be interrupted and said control point may be triggered.
[0084] The at least two answering points may be emergency call processing centres.
[0085] The control point may be a GSM service control point.
[0086] The network may further comprise a gateway location centre for providing an interface
between said network and said at least two answering points.
[0087] The control point may comprise a coordinate routing database for mapping a geographical
position of said first position estimate to said selected answering point.
[0088] The location centre may be located within said base controller.
[0089] The location centre may be located separate from said base controller.